This invention relates to magnetic read transducers capable of converting magnetic flux changes sensed from recorded media into assertive and complementary electrical signals.
Inductive magnetic heads are commonly employed to perform recording and reading of data. The constant demand for high recording density disk drives with smaller physical sizes, higher storage capacities and better performance requires manufacturers to build recording components that are capable of storing data with decreased data track widths and increased linear recording densities. This poses technical problems in the design and manufacture of magnetic transducers.
Magnetoresistive (MR) heads can read information on a record medium with much narrower data track widths and yield improved signal-to-noise ratio. The output signal generated during the data reading process is independent of the traveling speed of the recording medium. A typical MR head includes an MR sensor sandwiched between two magnetic shield layers. Disposed between the MR sensor and the magnetic shield layers are insulating layers. During the data reading mode, the magnetic shields act as magnetic flux guides confining the magnetic flux emanating from a record medium, and allow selected flux to be snsed by the MR sensor. Changes in magnetic flux correspondingly vary the resistivity of the MR sensor. A direct electric current passing through the MR sensor in turn generates a varying voltage which representss the information stored by the record medium.
In practice, miniaturized MR read heads experience various practical problems. For example, the MR layer in the magnetic head needs to be properly biased. The ferromagnetic MR layer at its natural state comprises a multiple number of magnetic domains separated by domain walls. These domain walls are highly unstable. During normal operation, the constant merging and splitting of the domain walls generate undesirable signal noise, commonly called Barkhausen noise, which degrades the performance of the magnetic head. To suppress the signal noise, hard magnetic bias layers are normally attached to the ferromagnetic layer for the purpose of aligning the magnetic domains in a single domain configuration. Furthermore, to position the ferromagnetic layer in the linear operating region, another bias, called the transverse bias needs to be provided to the ferromagnetic layer. A soft adjacent layer formed of a material with relatively high resistivity and minimal MR response is disposed adjacent to and spaced from the ferromagnetic layer to provide the transverse bias.
For the above reasons, there is a need to provide magnetic transducers that can interact with storage media having narrow data tracks with high linear recording densities, yet sufficiently sensitive to sense only the data signals being read from the recorded magnetic medium without the undesirable signal noise.
It is an object of the invention to provide magnetic transducers miniaturized in size and capable of interacting with storage media having narrow data track widths and high linear recording densities.
It is another object of the invention to provide magnetic read transducers with high sensitivity for signal sensing yet capable of screening out undesirable signal noise.
It is yet another object of the invention to provide magnetic read transducers with simplicity in design and reduction in processing steps, thereby reducing manufacturing costs.
According to the present invention, a magnetic transducer includes an assertive transducer portion and a complementary transducer portion. Between the two transducer portions is a bias portion which comprises an antiferromagnetic layer providing different bias fields to the two transducer portions. In the first embodiment, the transducer portions are implemented and operated in the anisotropic MR (AMR) mode. In the second embodiment, the transducer portions operate as a giant MR (GMR) or spin valve sensor.
In the first embodiment, the bias portion includes an antiferromagnetic layer. Each of the assertive and complementary transducer portions includes first and second layers of ferromagnetic material, respectively. The antiferromagnetic layer is deposited between and in contact with the first and second ferromagnetic layers. Different directions of uniaxial anisotropy are induced in the first and second ferromagnetic layers during fabrication. The different directions of magnetization in the first and second layers are sustained by the interposed antiferromagnetic layer through the mechanism of exchange coupling. Each of the first and second layers of ferromagnetic material, being biased differently by the bias layer in different directions, varies in resistivity differently in response to changes in magnetic flux intercepted by the transducer. When bias currents are applied, the first and second layers correspondingly generate varying voltages as assertive and complementary versions of the electrical signal, respectively.
In the second embodiment, the bias portion includes an antiferromagnetic layer. The assertive transducer portion includes first and third layers of ferromagnetic material. The first layer is designated as the pinned layer and the third layer as the active layer. The first and third layers are spaced from each other through a nonmagnetic layer. The complementary transducer portion includes second and fourth layers of ferromagnetic material. The second layer is designated as the pinned layer and the fourth layer as the active layer. The second and fourth layers are also spaced from each other through another nonmagnetic layer. The layer of antiferromagnetic material, being disposed in contact with the first and second layers, biases the first and second pinned layers to different directions. However, the third and fourth active layers, having initial directions of uniaxial anisotropy angularly oriented differently with respect to the magnetization of the first and second pinned layers, respectively, varies in resistivity differently in response to changes in magnetic flux intercepted by the transducer. When bias currents are applied, the third and fourth layers correspondingly generate varying voltages as assertive and complementary versions of the electrical signal, respectively.
Transducers made in accordance with this invention are capable of generating assertive and complementary signals with common mode noise rejection, which provides noise screening. The assertive and complementary signal versions, superimposed on each other, essentially double the amplitude of the sensed signal. In effect, the output electrical signal generated from the transducers of this invention is nearly doubled in amplitude and is practically free of noise. Furthermore, there is only one layer, the antiferromagnetic layer, performing the various functions of a magnetic biasing layer and insulator for the assertive and complementary sensor. This unique feature enables the read transducer to be built with reduced total thickness through simplified processing steps. Transducers of the present invention operate successfully with narrow data track widths and high recording densities.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which like reference numerals refer to like parts.